1. Field of the Invention
The present invention relates to a rotation detector for detecting a rotation speed of a rotating body, which is used for a vehicle, an airplane, a machine tool, or the like.
2. Description of the Related Art
Japanese Patent Unexamined Publication No. Hei. 2-116753 discloses a conventional rotation detector. FIG. 4 of the publication showing the prior art discloses a rotation detecting device in which a pair of magnetic detecting elements are disposed in the vicinity of a magnetic substance rotating together with a rotating body, the respective magnetic detecting elements are connected through their respective signal processing circuits to a detecting circuit, and the rotation direction of the rotating body is detected by using phase differences of pulses generated by the pair of magnetic detecting elements.
In this rotation detecting device, the respective magnetic detecting elements are connected through the respective signal processing circuits to the detecting circuit so that the number of the required signal processing circuits is the same as that of the magnetic detecting elements. Further, the number of required signal detection lines from the detecting circuit is also the same. Thus, a circuit structure around the rotation detecting device becomes complicated.
In FIGS. 2 and 3 of the publication disclosing the prior art, there is disclosed a rotation detector in which a gear portion of a magnetic substance set on a rotating body is asymmetrically-shaped, and waveforms of signals generated are analyzed to detect the rotation direction of the rotating body.
However, in this prior art, since the magnetic substance must be machined asymmetrically, this detector has a problem in that the machining cost becomes high. Moreover, if the number of teeth is large, formation of the gear shape is difficult and a limitation occurs in resolution. Further, in the detecting circuit, two thresholds are required for determination of the rotation direction, so that the amplitude of an output signal must be wide.